1. Field of the Invention Application
This invention relates to the field of valve assemblies for controlling the flow of material through a duct such as a pipeline, outlet of a cyclone, nozzle, and the like. The invention is particularly suitable for controlling spiralling flows of abrasive material or slurries in a pipeline or at the outlet of a cyclone.
2. Background of the Prior Art
Past valve assemblies for controlling the size of an opening in a duct such as a pipeline, outlet for a cyclone, nozzle, and the like have included slide valves such as U.S. Pat. Nos. 2,964,304 to Rice, issued Dec. 13, 1960, and 3,545,735 to Wolf, issued Dec. 8, 1970; rotary valves such as U.S. Pat. No. 3,179,471 to Savage, issued Apr. 20, 1965; weight actuated dump valves such as U.S. Pat. No. 2,792,910 to Redniss, issued May 21, 1957; iris valves with valve elements movable in a plane perpendicular to the flow such as U.S. Pat. Nos. 3,159,179 to DeLain, issued Dec. 1, 1964, 2,735,664 to Gamble, issued Feb. 21, 1956, and 2,649,272 to Barbato, issued Aug. 18, 1953; and valve assemblies in which the movable valve elements extend for a distance in the direction of the flow such as U.S. Pat. Nos. 3,183,776 to Wallis, issued May 18, 1865, 2,094,707 to Jones, issued Oct. 15, 1937, 2,770,944 to Jordan, issued Nov. 20, 1956, 3,136,525 to Creasser, issued June 9, 1964, 3,805,609 to Sato, issued Apr. 23, 1974, 2,726,509 to Gist, issued Dec. 13, 1955 and 2,926,489 to Halford, issued Mar. 1, 1960. Other assemblies having movable elements that extend in the direction of the flow and slide relative to each other include U.S. Pat. Nos. 497,903 to Woodward issued May 23, 1893, 3,226,768 to Zelewsky issued Jan. 4, 1966, and 3,618,925 to Girolami issued Nov. 9, 1971.
Valve designs that move the valve elements in a plane perpendicular to the flow such as U.S. Pat. Nos. 2,735,664 to Gamble, 2,649,272 to Barbato and 3,159,179 to DeLain create excessive turbulence in the flow. Further, if the material being conveyed through the ducts exerts a relatively high force on the valve elements or if the material is abrasive as in a silica and slurry, these valve elements tend to become misaligned or worn away and the control and sealing properties of the valves are greatly diminished. Valve designs with valve elements that seal along line contacts such as U.S. Pat. Nos. 3,136,525 to Creasser, 2,770,944 to Jordan and 2,094,707 to Jones have these same problems if the material being conveyed exerts high pressure on the valve elements or if the material is abrasive. Valve designs with valve elements that extend in the direction of the flow and overlap tend to operate better. In these designs, the sealing contact between each valve element extends over an area rather than a mere line contact. U.S. Pat. Nos. 497,903 to Woodward and 3,618,925 to Girolami illustrate such assemblies in which a plurality of overlapping valve elements slide relative to each other along their entire length. In these assemblies, a portion of each valve element is slidably mounted in a support. U.S. Pat. No. 3,226,768 to Zelewsky shows an assembly in which prismatic valve elements slide over a portion of each other as each valve element is moved axially to close the assembly. U.S. Pat. Nos. 2,926,489 to Halford and 2,726,509 to Gist illustrate valves with overlapping valve elements in which both ends of every other valve element are exposed to the flow. With such designs, if the material is spiralling through the duct, it will quickly wear away one exposed end of every second valve element and greatly diminish the sealing properties of the valve.
Problems with spiralling flows of abrasive material occur repeatedly in a duct at the outlet of a cyclone that is handling slurries or particulate matter such as sand. Valve assemblies at the outlet of a cyclone not only need to be long lasting and wear resistant but also need to be good control valves. They should close uniformly around the periphery of the outlet opening of the cyclone so that the opening becomes progressively smaller and uniformly tapers to a point.